Repairing defects in manufactured assemblies costs industries hundreds of millions of dollars each year. In fact, many industries view repairing defects in assemblies constructed of relatively thin metallic sheet materials, and the very high cost of these repairs, as a necessary evil and have invested heavily in preventing such defects rather than identifying more cost effective ways to repair such defects. The aircraft industry is just one of many industries plagued by this problem.
In the aircraft industry, parts are often manufactured to very exacting tolerances. As such, penetrations in aircraft parts are generally not made until after the part is manufactured and meets the predetermined tolerances. Such penetrations may be required for the insertion of bolts, or rivets, or as a means for cooling the part. One can easily appreciate that many of the hundreds of thousands of such penetrations in an aircraft are misplaced during assembly despite even the most exacting quality control measures. Such undesired holes, or material defects, then need to be repaired, while minimizing negative effects to the part. Additionally, the need frequently arises to repair damaged, corroded, or worn holes in parts that have already been in service for a period of time.
The aircraft industry, as well as virtually all industries that experience similar problems, currently relies upon arc welding and friction plug welding to repair such defects. Arc welding repair of relatively thin sheet metallic substrates requires a very skilled welder. Additionally, no matter how skilled the welder, the very nature of arc welding results in a large amount of heat input that is applied asymmetrically over the defect to repair the defect. As such, arc welding repairs have large heat affected zones that can influence mechanical and corrosion performance in the repair area. The large heat affected zone often results in local distortion of the repaired substrate that then requires post-weld treatment to return the substrate to the desired tolerances. A further limitation to arc welding repairs is the significant amount of pre and post-weld preparation of the defect area required to produce a quality weld and ensure the desired part geometry is produced.
An even greater limitation introduced when using arc welding to repair defects is that the repair weld is often of less than optimal quality and that filler materials must often be used that reduce performance of the component to improve the weldability of the surrounding substrate. This can result in repairs of significantly less strength than the surrounding substrate. For instance, filler metals having very high ductility, but less than desired strength and corrosion properties, are often required to minimize solidification cracking when using arc welding to repair defects in materials that have been in use for a period of time and suffer from reduced ductility. This is particularly true in the aircraft industry where holes often require repair after the aircraft has been in service for several years. In such repairs it is not uncommon that filler metals having strengths of 60% of the strength of the adjoining parent material are required so as to avoid solidification cracking of the weld repair.
As previously mentioned, friction plug welding has also been used to repair defects and holes in manufactured assemblies. Friction plug welding offers some advantages over the previously mentioned arc welding method in that it is a solid state process and produces a narrower heat affected zone. This minimizes the influence on mechanical and corrosion properties of the finished product.
The friction plug welding process has some definite limitations, which are primarily associated with the need to apply and react the mechanical loads associated with this process. Friction welding uses a consumable plug that must be rotated at high rpm and then pressed into a tapered hole to produce the repair. As such, the consumable plug is generally much larger than needed to produce the repair so that the plug can be rigidly gripped to allow the transfer of high speed and large loads. The reaction of the loads induced into the component by the plug typically requires specialized rigid tooling. The friction welding equipment used to produce the weld is typically very large due to the rotational energy that must be applied to the plug and the axial load necessary to force the plug into the tapered hole. An additional limitation of friction plug welding is that it requires line of sight access to the repair area, thereby limiting it to only the most simple repairs. Further, friction plug welding equipment is expensive and less readily available than arc welding or resistance welding equipment.
The parent application of this application, namely Ser. No. 10/772,701; filed on Feb. 5, 2004; titled “Method for Repairing Defects in a Metallic Substrate using Welding;” advances the state of the art by introducing a new resistance welding technique that incorporates a consumable filler slug, and in some embodiments, a sacrificial retainer. The method outlined in the Ser. No. 10/772,701 application dramatically changed how defects are repaired, however some highly conductive materials require additional consideration to coalesce the consumable filler slug and adjacent metallic substrate into a liquid pool via transmission of a reasonable amount of electrical current. The present invention solves the problems encountered in repairing conductive substrates.
Additionally, several of the present inventors invented the conductive heat seam welding method described in U.S. Pat. No. 6,545,244. While conductive heat seam welding has solved countless welding problems, only recently has the present invention solved many issues surrounding the repair of defects in highly conductive substrates.
The instant invention addresses many of the shortcomings of the prior art and allows for previously unavailable benefits. A method of repairing defects in a substrate that overcomes many of the limitations of the prior art has long been needed. The method of the present invention is designed to reduce the need for a skilled welder to effect repairs, and to result in a repaired substrate having greatly improved material properties, while negating many of the limitations of prior repair techniques. The method accomplishes such improvements by utilizing a relatively low heat input applied over a very short period of time and cooling of the repaired substrate. Additional benefits of the present method arise from the substantially uniform application of heat to the repair region and the fact that it typically requires no special preparation of defects prior to repair. Further, the equipment used to produce the repair is common in many manufacturing facilities and is relatively inexpensive to procure and maintain.